In an image formation process by an electrophotographic system, an electrostatic latent image is formed on an inorganic photoreceptor such as selenium, a selenium alloy, cadmium sulfide and amorphous silicon or an organic photoreceptor using a charge generating agent and a charge transfer agent. The electrostatic latent image is developed with a toner, transferred to paper or a plastic film, and fixed to provide a visible image. The photoreceptor has a positive chargeability or a negative chargeability depending on its configuration. If a printed matter is left as the electrostatic latent image by exposure, it is developed with an opposite sign chargeable toner. On the other hand, if the printed matter is charge-removed and inverted, it is developed with a same sign chargeable toner.
The toner is configured of a binder resin, a coloring agent and other additives. In general, a charge control agent is added in order to add desirable charging properties (including a charging speed, a charging level and a charging stability), a temporal stability, and an environmental stability. By adding the charge control agent, the properties of the toner are greatly improved.
Examples of a positive friction chargeable charge control agent used in the technical field of interest include Nigrosine dye, azine based dye, a copper phthalocyanine pigment, a quaternary ammonium salt and a polymer having a quaternary ammonium salt in a side chain. On the other hand, as a negative friction chargeable charge control agent, a metal complex salt of monoazo dye, salicylic acid, naphthoic acid, a metal complex of dicarboxylic acid, a copper phthalocyanine pigment, and a resin including an acid component are used.
In a color toner of which market is expected to expand in the future, a light color that does not affect a hue, desirably a colorless, charge control agent is essential. Examples of the light color or colorless charge control agent for the negative chargeable toner include a metal complex salt compound of a hydroxybenzoic acid derivative (see Patent Documents 1 to 3, for example), a metal salt compound of aromatic dicarboxylic acid (see Patent Document 4, for example), a metal complex salt compound of an anthranilic acid derivative (see Patent Documents 5 to 6, for example), an organic boron compound (see Patent Documents 7 to 8, for example), a biphenol compound (see Patent Document 9, for example), a calix (n) arene compound (see Patent Documents 10 to 15, for example) and a cyclic phenol sulfide (see Patent Documents 16 to 18, for example). Examples of the positive chargeable toner include a quaternary ammonium salt compound (see Patent Documents 19 to 21, for example).
Patent Document 1: Japanese Patent Application Laid-open No. 55-042752
Patent Document 2: Japanese Patent Application Laid-open No. 61-069073
Patent Document 3: Japanese Patent Application Laid-open No. 61-221756
Patent Document 4: Japanese Patent Application Laid-open No. 57-111541
Patent Document 5: Japanese Patent Application Laid-open No. 61-141453
Patent Document 6: Japanese Patent Application Laid-open No. 62-094856
Patent Document 7: U.S. Pat. No. 4,767,688
Patent Document 8: Japanese Patent Application Laid-open No. 1-306861
Patent Document 9: Japanese Patent Application Laid-open No. 61-003149
Patent Document 10: Japanese Patent No. 2568675
Patent Document 11: Japanese Patent No. 2899038
Patent Document 12: Japanese Patent No. 3359657
Patent Document 13: Japanese Patent No. 3313871
Patent Document 14: Japanese Patent No. 3325730
Patent Document 15: Japanese Patent Application Laid-open No. 2003-162100
Patent Document 16: Japanese Patent Application Laid-open No. 2003-295522
Patent Document 17: PCT International Publication No. 2007-111346
Patent Document 18: PCT International Publication No. 2007-119797
Patent Document 19: Japanese Patent Application Laid-open No. 57-119364
Patent Document 20: Japanese Patent Application Laid-open No. 58-009154
Patent Document 21: Japanese Patent Application Laid-open No. 58-098742